1. Field of the Invention:
This invention relates to a method for the hydrogenation of coal tar pitch. Particularly, this invention relates to a method for the hydrogenation of coal tar pitch, specifically the conversion of coal tar pitch containing a large amount of toluene insolubles to slightly hydrogenated coal tar pitch useful as a carbonaceous raw material. More particularly, this invention relates to a method for commercially advantageous manufacture of a carbonaceous raw material possessing a structure having nuclei partially hydrogenated while retaining polycyclic condensation configuration intact, containing hetero atoms such as nitrogen, sulfur, oxygen, and metals at low concentrations, and possessing properties for needle coke, carbon fibers of high quality and pitch coke.
2. Description of the Prior Art:
It is known that tar pitch is excellent as a carbonaceous raw material for pitch coke, particularly needle coke and carbon fibers, is obtained by hydrogenating coal tar pitch. Generally, this hydrogenation is effected to a slight extent.
For example, it is disclosed in the specification of GB No. 2129825 that pitch is slightly hydrogenated as with tetrahydroquinoline for the production raw material for carbon fibers. In the specification of Japanese Patent Publication No. 49(1974)-11,602, it is stated that as a means of producing needle coke from coal tar pitch, slight hydrogenation performed on the pitch gives rise to tar pitch capable of producing needle coke excellent in quality.
In the hydrogenation of coal tar pitch, it is naturally a prerequisite that the hydrogenated product should possess high quality. Still more important is a crucial requirement that the hydrogenation carried out on a commerical scale should enable the product to be continuously obtained with stable quality over a long period of time. In the treatment of virgin-type heavy petroleum oil, the hydrogenation of slight degree as contemplated by this invention poses no problem concerning continuous protracted production. This is because, in the case of a heavy fraction of virgin oil, the main causes for deactivation of the catalyst used in the treatment reside chiefly in vanadium and nickel and the slight hydrogenation has no possibility of appreciably deactivating the catalyst and enables the product to be obtained with stable quality for a long time.
The coal tar pitch which this invention intends to use as the raw material has different nature from the heavy fraction of virgin oil. Unlike the heavy fraction of oil, coal tar pitch contains virtually no vanadium or nickel and avoids entailing deactivation of the catalyst by such heavy metals. It nevertheless contains, in large amounts, toluene insolubles (hereinafter referred to as "TI") which are contained very little in the heavy fraction of virgin type petroleum oil. This TI induces heavy deposition of carbon on the catalyst and in the interparticles of the catalyst and deactivates the catalyst very quickly so as to render continuous catalytic hydrogenation substantially impracticable.
If the TI is removed from the coal tar pitch for the prevention of the catalyst deactivation, the catalyst used in the hydrogenation enjoys an elongation in its service life. As described afterward, however, this treatment of coal tar pitch for removal of the TI obstructs fulfillment of the primary object of producing a carbonaceous raw material of high quality because it inevitably results in removal of those components which possess the basic structure of a polycyclic condensation configuration like TI and which are transformed after the partial hydrogenation into substances possessing properties of high quality for a carbonaceous raw material.
For the reasons given above, the slight hydrogenation of coal tar pitch carried out continuously in the presence of a catalyst for a long period encounters a serious hindrance. In the circumstance, a method which effects the hydrogenation by using such an expensive hydrogen donating solvent as tetrahydroquinoline instead of using any catalyst has been proposed as disclosed in GB No. 2129825, for example. The use of this hydrogen donating solvent not merely renders the treatment expensive but also tends to provide removal of hetero atoms and modification of quality by hydrogenation both insufficiently because the action of hydrogenation manifested on pitch is weak.
Japanese Patent Publication No. SHO 49(1974)-11,602 discloses catalytic hydrogenation. All the working examples cited therein invariably cover reactions carried out batchwise in an autoclave. No continuous operation performed for a long period is mentioned anywhere.
It is, therefore, extremely important to continue a study and develop a method which effects hydrogenation of pitch by using a catalyst of high performance capable of keeping a catalytic activity at a high level even on pitch without inducing deposition of carbon and the optimum conditions of hydrogenation incapable of deactivating the catalyst.